Sensing response of aluminum-side-polished fiber-based surface plasmon resonance sensors to surface roughness

Aluminum is a widely used and cost-effective material for marine equipment because of its strong adhesion and simple coating processes. This study utilizes finite element numerical analysis to examine the sensing characteristics and sensitivity of aluminum-side-polished fiber (SPF) surface plasmon resonance (SPR) sensors with varying aluminum film thicknesses. Additionally, it investigates the response characteristics of these sensors to different surface roughness morphologies. The simulation results reveal that for SPF-based SPR sensors with a remaining thickness of 1 μm under a wavelength of 1550 nm, the coupling depth of the SPR resonance peak initially deepens and then shallow increases as the aluminum film thickness increases from 20 nm to 50 nm, achieving maximum coupling depth and sensitivity of 857 nm/RIU at 30 nm thickness. Models of aluminum-SPF-based SPR sensors were developed for ideally smooth, periodically rough, and randomly rough surface morphologies. The simulations reveal that as the surface morphology of the fiber transitions from smooth to periodically rough to randomly rough, the SPR resonance peak shifts from 961 nm to 954 nm and then to 885 nm, with the blue shift range increasing as the random roughness of the fiber surface intensifies. These simulations confirm the efficacy of aluminum-SPF-based SPR sensors in detecting variations in surface roughness morphology, establishing a theoretical foundation for the further application of these sensors in developing new sensing platforms for detecting corrosion in marine equipment materials in marine environments.